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A discount is not a marketing expense. Every unit of discount comes straight out of contribution margin—the narrow slice left after COGS and variable costs. That is why sales must rise far more than the discount percentage to keep profit unchanged.

This tool shows what your planned discount does to per-unit margin, how many times sales must grow to keep profit the same, and how much less you have left at period end if sales do not reach that level. If the discount drives margin to zero or negative, instead of a figure it says plainly that no volume can make up for it.

• Contribution margin per unit before discount = current price − unit COGS − other variable costs per unit. If you enter a percentage margin instead of COGS, COGS is reconstructed from it: price × (1 − margin ÷ 100).
• Discount amount per unit = price × discount percent. Margin after = margin before − that amount; no part of the discount is offset elsewhere.
• Break-even volume factor = margin before ÷ margin after. This comes from equating "quantity before × margin before = quantity after × margin after"; the required increase % is (factor − 1) × 100.
• If the discount applies only to part of sales, average margin across all units goes in the denominator instead of discounted-unit margin: margin before − discounted sales share × discount amount.
• When margin after is zero or negative, the denominator is not positive and the factor is undefined: the tool does not show infinity; it says no sales volume can offset this discount.
• The sensitivity table repeats this multiplier for 5, 10, 15, 20, 25, and 30 percent discounts; the scenario table answers the reverse: at this discount, if sales rise 0, 25, 50, or 100 percent, what is period contribution profit.
• Period fixed cost is used only in the two "operating effect" lines and only when you have also entered period sales quantity; it plays no role in per-unit margin or the volume factor.

• This tool outputs "contribution profit", not net profit: fixed costs, tax, and financing are not in margin per unit. Even when an operating effect is shown, it is still not net profit.
• The base assumption is that unit COGS does not change with volume. If larger purchases earn buying discounts, true breakeven volume is a little lower than this figure; if more sales need extra staff or warehouse space, higher.
• The volume factor means "profit does not fall", not "this is the right move": production and supply capacity, opportunity cost and the discount's effect on customers' price perception are in none of the figures here.
• The effect of the discount on sales of other products and changes in basket mix is not calculated; if discounting one item shifts sales from a more expensive item, this tool does not see that.
• This tool is a calculator, not advice: none of the figures is a pricing or investment recommendation, and example figures are hypothetical.